Between an unmodded original 6 car PB (C7030) and the new APB (C7042) there's no contest. Get the C7042.
If you ALREADY had a PB-Pro unit with Simple-H, then I'd tell you to stick with that a while longer, as it's still plenty good, equal to the APB, better in some respects.
If you're asking should you get the APB or mod your C7030, I'll probably still go with the APB. The only reason for that is that future development will focus on that, and unless Andy S is able to give PB-Pro users the SNC mode, it's likely to get left behind, especially once Simple-H comes out for the APB (what's the hold up, guys? ;-)), and they figure out how to make the APB display or the RichG Lap Display work with the APB while also connected to a computer. Maybe a new Lap display will be created instead, I don't know.
So, the future of both is still somewhat unknown, but as the APB is being produced now, and the C7030 is not, it's likely that the APB will have the longer lifetime starting from now.
Oh, and the PSUs you have for your two 4 car bases are exactly what you need for the APB.
Also, PB-Pro is cheaper than an APB, but unless you only ever have two or three cars on the track, you'll want to add the Simple-H upgrade, which brings the total price up to more than the APB, especially since you don't also need to buy PSUs for the APB... and you might need one for a PB-Pro SH.